The present invention relates to a gelled aqueous composition comprising a block copolymer containing at least one water-soluble block and one hydrophobic block.
Amphiphilic molecules are molecules having different water-solubility regions which give them special properties. A known example of an amphiphilic molecule is that of surfactants which may have a hydrophilic and a hydrophobic region.
Because of their amphiphilic character, these molecules come together and organize themselves in solution in water to form micelles. These micelles may be of various morphologies, such as spherical micelles or anisotropic micelles (for example lamellar or vermicular micelles). Spherical micelles are the most common as they are the most accessible.
These micelles are in equilibrium, which means that dilution or addition of a solvent or of a cosurfactant to the medium containing these micelles results in a variation in the size of the micelles or in their morphology.
One objective of the present invention is to provide amphiphilic block copolymers of hydrophobic/hydrophilic structure which can form a gel when they are in water.
Another objective is to be able to obtain easily preparable aqueous gels whose elastic modulus can be adjusted.
To achieve the above objectives, the purpose of the invention is the use of a block copolymer containing at least one block water-soluble in nature and at least one block predominantly hydrophobic in nature, which copolymer is in the form of micelles when it is in water.
This block copolymer forms a viscoelastic gel when it is in solution in water.
This block copolymer contains at least one block predominantly hydrophobic in nature and at least one water-soluble block, the predominantly hydrophobic block having hydrophilic units preferably in an amount of less than 33% by weight with respect of the total weight of the units of said predominantly hydrophobic block. This amount may be equal to 0 but is preferably at least 1% by weight and less than 25% by weight, even more preferably between 2 and 15%, with respect to the total weight of the units of said predominantly hydrophobic block.
This block copolymer contains at least one block predominantly hydrophobic in nature and at least one water-soluble block, the water-soluble block having hydrophobic units in an amount which may be small, about 1% of the total weight of the units of said water-soluble block. The maximum amount of hydrophobic units depends on the nature of the units and is in most cases less than 70% by weight and at least 1% by weight, and even more preferably less than 50% by weight and at least 10%, with respect to the total weight of the units of said water-soluble block.
The invention also relates to a process for preparing these block copolymers by so-called living or controlled polymerization.
The invention also relates to a process for controlling the hydrophilic/hydrophobic balance of amphiphilic block copolymers having at least one block coming from the polymerization of hydrophilic monomers and at least one block coming from the polymerization of hydrophobic monomers, in which process:
hydrophilic units are introduced into the block coming from the polymerization of hydrophobic monomers, and/or
hydrophobic units are introduced into the block coming from the polymerization of hydrophilic monomers.
Finally, the invention relates to the use of these block copolymers as gelling agents or as thickeners for aqueous medium.
The invention firstly therefore relates to a block copolymer containing at least one block water-soluble in nature and at least one block predominantly hydrophobic in nature. According to a first embodiment, the copolymer contains only a single hydrophobic block and a single water-soluble block. According to another embodiment, the copolymer contains a water-soluble block having a hydrophobic group at each end or vice-versa.
In the description which follows, the expression xe2x80x9cblock water-soluble in naturexe2x80x9d should be understood to mean a polymer block containing a number of hydrophilic groups sufficient to obtain a water soluble block well dissolved in water. Solubility in water of the water soluble block means a block copolymer containing such a water-soluble block, when mixed with water, gives a translucent monophasic system. Usually such a translucent monophasic system is obtained from a water soluble block comprising at least 30%, preferably at least 50% by weight of hydrophilic units with respect to the totality of units of the water-soluble block. The block water-soluble in nature is therefore soluble in water. The term xe2x80x9cunitxe2x80x9d should be understood to mean that part of the block corresponding to a monomeric unit.
Likewise, the expression xe2x80x9cblock predominantly hydrophobic in naturexe2x80x9d should be understood to mean a polymer block preferably containing at least 67% by weight hydrophobic units with respect to the totality of units. The block predominantly hydrophobic in nature is not soluble in water. This block copolymer containing at least one block water-soluble in nature and at least one block predominantly hydrophobic in nature forms a viscoelastic gel when it is in solution in water.
The term xe2x80x9cviscoelastic gelxe2x80x9d should be understood to mean a liquid medium for which the viscous modulus Gxe2x80x3 and the elastic modulus Gxe2x80x2 are such that Gxe2x80x2 greater than Gxe2x80x3. This gel behaviour is manifested by a flow threshold and even, in some cases, by a shear-thickening effect (an increase in the viscosity with flow). This gel effect is obtained when the polymer concentration exceeds a certain threshold called the critical gelling concentration.
The block copolymers according to the present invention have the advantage of making the aqueous media viscoelastic when they are used in only a small amount with respect to the aqueous medium. The copolymer is preferably used at a concentration higher than 0.1% by weight and even more preferably at a concentration from 1 to 10% by weight.
The properties of the copolymers according to the present invention may be obtained by selecting the nature of the soluble blocks and the nature of the predominantly hydrophobic blocks, at least the hydrophilic block having to contain hydrophobic groups in an appropriate amount.
According to one embodiment of the invention, the weight ratio of the block water-soluble in nature to the completely hydrophobic block is between 95/5 and 20/80, even more preferably between 90/10 and 40/60.
According to a first version of the preparation, the blocks water-soluble in nature and the blocks predominantly hydrophobic in nature of the above copolymers may come from the copolymerization of hydrophilic and hydrophobic monomers. The amounts of hydrophilic and hydrophobic units in each of the said blocks can then be controlled by the respective contents of hydrophilic monomers and hydrophobic monomers during the polymerization of the blocks.
Thus, the blocks predominantly hydrophobic in nature may come from the copolymerization of hydrophobic monomers and of hydrophilic monomers, the hydrophilic monomers being present in an amount of less than 33% by weight, preferably at least 1% by weight, even more preferably between 2 and 15%, with respect to the total weight of the units of the hydrophobic block.
In addition, the blocks water-soluble in nature may come from the copolymerization of hydrophilic monomers and of hydrophobic monomers, the hydrophobic monomers being present in an amount of less than 70% by weight, preferably at least 1% by weight, even more preferably between 50 and 25%, with respect to the total weight of the units of the water-soluble block.
According to a second version of the preparation, the blocks water-soluble in nature may come:
from the polymerization of monomers that may be rendered hydrophilic by hydrolysis and optionally of non-hydrolysable hydrophobic monomers and/or of hydrophilic monomers, and then
from the hydrolysis of the polymer obtained.
During the hydrolysis, the units corresponding to the hydrolysable monomers are hydrolysed into hydrophilic units.
The amounts of hydrophilic and hydrophobic units in each of the said blocks are then controlled by the amount of each type of monomer and by the degree of hydrolysis.
According to this second version, various methods of implementation may be envisaged.
According to a first method of implementation, the blocks may be obtained by:
homopolymerization of hydrophobic monomers that can be rendered hydrophilic by hydrolysis and
partial hydrolysis of the homopolymer obtained to a degree such that what is obtained is:
either, in the case of the blocks predominantly hydrophobic in nature, an amount of hydrophilic units of less than 33% by weight, preferably at least 1% by weight, even more preferably between 2 and 15%, with respect to the total weight of the units of the hydrophobic block.
or, in the case of the blocks water-soluble in nature, an amount of hydrophobic units of less than 70% by weight, preferably at least 1% by weight, even more preferably between 25 and 50%, with respect to the total weight of the units of the water-soluble block.
According to a second method of implementation, the blocks may be obtained by:
copolymerization of hydrophobic monomers that can be rendered hydrophilic by hydrolysis and of hydrophobic monomers that cannot be rendered hydrophilic by hydrolysis and then
complete or partial hydrolysis of the polymer obtained.
According to this second method of implementation, the amount of hydrophilic and hydrophobic units may depend on two criteria, namely the content of the various types of monomers and the degree of hydrolysis.
If there is complete hydrolysis, it is sufficient to vary the content of the monomers and thus:
the blocks predominantly hydrophobic in nature can come:
from the polymerization of a mixture of hydrophobic monomers that can be rendered hydrophilic by hydrolysis and of hydrophobic monomers that cannot be rendered hydrophilic by hydrolysis, the hydrophobic monomers that can be rendered hydrophilic by hydrolysis being present in an amount of less than 33% by weight, preferably at least 1% by weight, even more preferably between 2 and 15%, with respect to the total weight of the units of the hydrophobic block, and then
from the complete hydrolysis of the polymer obtained;
the blocks water-soluble in nature may come:
from the polymerization of a mixture of hydrophobic monomers that can be rendered hydrophilic by hydrolysis and of hydrophobic monomers that cannot be rendered hydrophilic by hydrolysis, the hydrophobic monomers that cannot be rendered hydrophilic by hydrolysis being present in an amount of less than 70% by weight, preferably at least 1% by weight, even more preferably between 50 and 25%, with respect to the total weight of the units of the water-soluble block, and then
from the complete hydrolysis of the polymer obtained.
If there is partial hydrolysis, the monomer content and the degree of hydrolysis may be varied at the same time.
According to a third method of implementation, the blocks may be obtained by:
copolymerization of hydrophobic monomers that can be rendered hydrophilic by hydrolysis and of hydrophilic monomers and then
partial hydrolysis of the polymer obtained to a degree such that what is obtained is:
either, in the case of the blocks predominantly hydrophobic in nature, an amount of hydrophilic units of less than 33% by weight, preferably at least 1% by weight, even more preferably between 2 and 15%, with respect to the total weight of the units of the hydrophobic block.
or, in the case of the blocks water-soluble in nature, an amount of hydrophobic units of less than 70% by weight, preferably at least 1% by weight, even more preferably between 50 and 25%, with respect to the total weight of the units of the water-soluble block.
In general, the hydrophobic monomers may be chosen from:
vinylaromatic monomers, such as styrene,
dienes, such as butadiene,
alkyl acrylates and methacrylates the alkyl group of which contains from 1 to 10 carbon atoms, such as methyl, ethyl, n-butyl, 2-ethylhexyl, tert-butyl, isobornyl, phenyl and benzyl acrylates and methacrylates.
Preferably, it is styrene.
The hydrophilic monomers may be chosen from:
ethylenically unsaturated carboxylic acids such as acrylic and methacrylic acids;
neutral hydrophilic monomers such as acrylamide and its derivatives (N-methylacrylamide, N-isopropylacrylamide), methacrylamide, polyethylene glycol methacrylate and polyethylene glycol acrylate;
anionic hydrophilic monomers: sodium 2-acrylamido-2-methylpropanesulphonate (SAMPS), sodium styrenesulphonate and sodium vinylsulphonate.
The monomers that can be rendered hydrophilic by hydrolysis may be chosen from:
acrylic and methacrylic esters hydrolysable in acid, such as methyl acrylate, ethyl acrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate and tert-butyl acrylate;
vinyl acetate hydrolysable into vinyl alcohol units;
quaternized 2-dimethylaminoethyl methacrylate and acrylate (quatdamma and quatdama);
acrylamide and (meth)acrylamide.
Preferably, the block copolymers according to the invention are diblock copolymers. However, they may also be triblock, or even multiblock copolymers. If the copolymer comprises three blocks, it is preferable to have a block water-soluble in nature flanked by two blocks predominantly hydrophobic in nature.
According to a particular embodiment of the invention, the copolymer is a diblock copolymer comprising a block water-soluble in nature and a block predominantly hydrophobic in nature, in which:
the block water-soluble in nature contains acrylic acid (AA) units and ethyl acrylate (EtA) units and
the block predominantly hydrophobic in nature contains styrene (St) units and methacrylic acid (MAA) and/or hydroxyethyl methacrylate (HEMA) units.
Preferably, according to this embodiment, the block water-soluble in nature comes:
from the polymerization of methacrylic acid (MAA) and of ethyl acrylate (EtA) in an EtA/MAA weight ratio from 90/10 to 99/1, and then
from the hydrolysis of the polymer obtained to a degree of at least 50 mol% up to 95 mol%.
Preferably, the block predominantly hydrophobic in nature comes from the polymerization of a monomer mixture comprising at least 80% by weight styrene.
Generally, the block copolymers according to the invention have a molecular mass of at most 100,000 g/mol, preferably at least 1000 g/mol.
In general, the above block copolymers can be obtained by any so-called living or controlled polymerization process such as, for example:
radical polymerization controlled by xanthates according to the teaching of Application WO 98/58974,
radical polymerization controlled by dithioesters according to the teaching of Application WO 97/01478,
polymerization using nitroxide precursors according to the teaching of Application WO 99/03894,
radical polymerization controlled by dithiocarbamates according to the teaching of Application WO 99/31144,
atom transfer radical polymerization (ATRP) according to the teaching of Application WO 96/30421,
radical polymerization controlled by iniferters according to the teaching of Otu et al., Makromol. Chem. Rapid. Commun., 3, 127 (1982),
radical polymerization controlled by degenerative iodine transfer according to the teaching of Tatemoto et al., Jap. 50, 127, 991 (1975), Daikin Kogyo Co Ltd., Japan and Matyjaszewski et al., Macromolecules, 28, 2093 (1995),
group transfer polymerization according to the teaching of O. W. Webster xe2x80x9cGroup Transfer Polymerizationxe2x80x9d, pp. 580-588 in xe2x80x9cEncyclopedia of Polymer Science and Engineeringxe2x80x9d, vol. 7 and H. F. Mark, N. M. Bikales, C. G. Overberger and G. Menges, Publ., Wiley Interscience, New York, 1987,
radical polymerization controlled by tetraphenylethane derivatives (D. Braun et al., Macromol.Symp. 111,63 (1996)), and
radical polymerization controlled by organocobalt complexes (Wayland et al., J.Am.Chem.Soc. 116,7973 (1994)).
The preferred polymerization is living radical polymerization using xanthates.
The invention therefore furthermore relates to a process for preparing these block copolymers. This process consists in:
1xe2x80xa2 the following being brought into contact with one another:
at least one ethylenically unsaturated monomer,
at least one source of free radicals and
at least one compound of formula (I): 
in which:
R represents an R2Oxe2x80x94, R2Rxe2x80x22Nxe2x80x94 or R3xe2x80x94 group, where: R2 and R xe2x80x22, which are identical or different, represent (i) an alkyl, acyl, aryl, alkene or alkyne group or (ii) a saturated or unsaturated, possibly aromatic, carbocycle or (iii) a saturated or unsaturated heterocycle, these groups and rings (i), (ii) and (iii) possibly being substituted,
R3 represents H, Cl, an alkyl, aryl, alkene or alkyne group, a saturated or unsaturated, optionally substituted (hetero) cycle, an alkylthio, alkoxycarbonyl, aryloxycarbonyl, carboxy, acyloxy, carbamoyl, cyano, dialkylphosphonato, diarylphosphonato, dialkylphosphinato or diarylphosphinato group, or a polymer chain,
R1 represents (i) an optionally substituted alkyl, acyl, aryl, alkene or alkyne group or (ii) an optionally substituted or aromatic, saturated or unsaturated, carbocycle or (iii) an optionally substituted, saturated or unsaturated, heterocycle, or a polymer chain;
2xe2x80xa2 the above contacting operation being repeated at least once, using:
monomers differing from those in the previous operation, and
instead of the precursor compound of formula (I), the polymer coming from the previous operation; and
3xe2x80xa2 optionally, the copolymer obtained being hydrolysed.
The R1, R2, Rxe2x80x22 and R3 groups may be substituted with alkyl groups, substituted phenyls, substituted aromatic groups or one of the following groups: oxo, alkoxycarbonyl or aryloxycarbonyl (xe2x80x94COOR), carboxy (xe2x80x94COOH), acyloxy (xe2x80x94O2CR), carbamoyl (xe2x80x94CONR2), cyano (xe2x80x94CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, isocyanate, phthalimido, malexc3xafmido, succinimido, amidino, guanidimo, hydroxyl (xe2x80x94OH), amino (xe2x80x94NR2), halogen, allyl, epoxy, alkoxy (xe2x80x94OR), S-alkyl, S-aryl, silyl, groups having a hydrophilic or ionic character, such as alkali metal salts of carboxylic acids, alkali metal salts of sulphonic acid, polyoxy alkylene (POE, POP) chains, and cationic substituents (quaternary ammonium salts), R representing an alkyl or aryl group.
Preferably, the compound of formula (I) is a dithiocarbonate chosen from compounds of the following formulae (IA), (IB) and (IC): 
in which:
R2 and R2xe2x80x2 represent (i) an alkyl, acyl, aryl, alkene or alkyne group, or (ii) an optionally aromatic, saturated or unsaturated, carbocycle or (iii) a saturated or unsaturated heterocycle, these groups and rings (i), (ii) and (iii) possibly being substituted;
R1 and R1xe2x80x2 represent (i) an optionally substituted alkyl, acyl, aryl, alkene or alkyne group or (ii) an optionally substituted or aromatic, saturated or unsaturated, carbocycle or (iii) an optionally substituted, saturated or unsaturated, heterocycle, or a polymer chain;
p is between 2 and 10.
During step 1, a first block of the copolymer is synthesized so as to become water soluble or hydrophobic in nature depending on the nature and the amount of monomers used. During step 2, the other block of the polymer is synthesized.
The ethylenically unsaturated monomers will be chosen from the hydrophilic, hydrophobic and hydrolysable monomers defined above, in proportions suitable for obtaining a block copolymer whose blocks have the characteristics of the invention. According to this process, if all the successive polymerization steps are carried out in the same reactor, it is generally preferable for all the monomers used during one step to have been consumed before the polymerization of the next step starts, therefore before the new monomers have been introduced. However, it may happen that the hydrophobic or hydrophilic monomers of the previous step are still present in the reactor during the polymerization of the next block. In this case, these monomers generally represent no more than 5 mol % of all the monomers and they participate in the following polymerization by contributing to introducing hydrophobic or hydrophilic units into the next block.
For more details with regard to the above polymerization processes, the reader may refer to the contents of Application WO 98/58974.
The hydrolysis may be carried out using a base or an acid. The base may be chosen from alkali or alkaline-earth metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal alcoholates, such as sodium methylate, sodium ethylate, potassium methylate, potassium ethylate and potassium tert-butylate, ammonia and amines such as triethylamines. The acids may be chosen from sulphuric acid, hydrochloric acid and paratoluenesulphonic acid. It is also possible to use an ion-exchange resin or an ion-exchange membrane of the cationic or anionic type. The hydrolysis is generally carried out a temperature of between 5 and 100xc2x0 C., preferably between 15 and 90xc2x0 C.
After hydrolysis, the block copolymer can be washed, for example by dialysis against water, or using a solvent such as alcohol. It may also be precipitated by lowering the pH below 4.5.
The hydrolysis may be carried out on a monoblock polymer, which will then be linked to other blocks, or on the final block copolymer.
The invention also relates to a process for controlling the hydrophilic/hydrophobic balance of amphiphilic block copolymers having at least one block coming from the polymerization of hydrophilic monomers and at least one block coming from the polymerization of hydrophobic monomers, in which:
hydrophilic units are introduced into the block coming from the polymerization of hydrophobic monomers, and/or
hydrophobic units are introduced into the block coming from the polymerization of hydrophilic monomers.
Finally, the invention relates to the use of the above block copolymers as a gelling agent or as a thickening agent in aqueous and organic media. Preferably, the polymers have to be used in a concentration of at least 0.1% by weight and of at most 20%, even more preferably 0.5 to 10% by weight in said aqueous and organic media. The block copolymers according to the invention therefore have the advantage of allowing gelling in liquid media by being used in very low concentration. Consequently, the cost of using them is lower and they have little or no influence on the properties of the gelled medium.
The following examples illustrate the invention without however limiting its scope.